We demonstrated that human and rat red blood cells (RBC) contain catecholamines (CA), namely, norepinephrine (NE), epinephrine (E) and dopamine (DA), also CA metabolites, normetanephrine (NM), dihydroxymandelic acid (DOMA) and dihydroxyphenylethylene glycol (DOPEG) and the amine, octopamine (OA). We also observed that RBC concentrations of some of these substances changed during sympathoadrenal activation. Aims of the proposed studies are: to quantify the in vivo rates of CA accumulation by RBC, steady state concentrations and RBC half-life of CA during and after I.V. infusions of CA; to quantify the chronic changes in RBC CA during development of rat pheochromocytoma and the RBC half-life of CA after tumor removal; to measure simultaneous changes of CA metabolites during the same studies; to determine if CA metabolites and if E are formed inside RBC; and to assess RBC as a model of non-neuronal CA uptake. CA and CA metabolites in plasma and RBC lysate are measured by sensitive, specific, radio- enzymatic, thin-layer chromotographic assays. Pheochromocytoma tumor-bearing rats are produced by tumor tissue implantation into a special strain of rats. RBC accumulation rates and half-lives of CA will be determined from regression analysis of data obtained during and after acute I.V. infusions of NE, E or DA into rabbits, rats and humans, during acute tumor manipulation and after tumor removal. Activity of catabolic enzymes, COMT and MAO will be studied in RBC lysate of tumor-bearing rats. RBC accumulation of CA will be studied after infusion or injection of non-neuronal blockers of CA uptake, namely, corticosterone, beta-estradiol and metanephrine. These studies will contribute new information regarding inactivation and disposition of biogenic amines and will develop data on a previously unrecognized role of RBC in these processes.